F3 AA or F3 AB ?

It doesn't really matter. The RR used what was available to fit the load. Me I would always choose an AA first.

Typically, an A-A consist would be more common for two units, especially on the NYC.  The booster units would be added as needed for additional tonnage or longer trains, while the A-A consist would provide more flexibility in that the locomotives would not need to be turned at the end of a run.  Furthermore, much like arch competitor the PRR, NYC would run booster units as part of an A-B-A consist.  NYC followed a similar practice with passenger trains - A-A units on trains or if needed an A-B-A consist.

Where I have seen A units paired with B units only has been more common on passenger trains on the western roads.  Santa Fe purchased A-B-B F7s in the 300 series for passenger trains while many of their passenger trains operated as A-B units.  SP followed similar practices of A-B units for passenger trains. 

One resource is to look at the number of rostered F3s in the A and B configurations and you will see that booster cab units outnumbered booster units by a fairly sizeable margin in most cases.

However, it is your layout so your practices are what matters most.  I like A-B configurations for passenger trains as I don't need to set the unit to run in reverse in command for my 3 rail trains. 

Hope that helps!

I run AB as much as AA because I have quite a few powered B's.  Not prototypical but ABA and ABBA feels like to much locomotive power when compared to the 8 to 12 cars I usually pull.  It's just my personal preference.

@Jim 1939 posted:

It doesn't really matter. The RR used what was available to fit the load. Me I would always choose an AA first.

I concur… the NYC ran them both ways, and so do I.  If I’m up for a quick run, Lionel F3As it is as they’re both in the same box.  With that said, my Atlas F2A gets a B, as does the Lionel F7A.

thanks!

- Mario

Great responses.

I have all steam locos except for a two engine set of NYC F3 AAs and a separate F3 B unit.  Since my layout is very small, for now, I will never run them as ABAs but may run them as an AA or AB.

I think I'll pull out the A units and keep the B in storage. Eventually the As will receive ERR Cruise and Sound.

Thanks

Ward

A few years ago Atlas did not make an AB in B&O because as Bob Thatcher said, it wasn't prototypical.  With MTH coming out with a B unit, if the colors match I will get one.  My railroad, my rules.  I typically buy ABA with only one A powered.

John

The advice above is all good.  I am adding this link as the table towards the bottom can maybe help others with a similar question of other RR's.  Note a few RR's never even bought B's.

https://en.wikipedia.org/wiki/EMD_F3

BTW if you ever decide to go with FT's many were draw bar linked!

@jbmccormick posted:

A few years ago Atlas did not make an AB in B&O because as Bob Thatcher said, it wasn't prototypical.  With MTH coming out with a B unit, if the colors match I will get one.  My railroad, my rules.  I typically buy ABA with only one A powered.

John

The B&O did have F3 B units. The MTH model is excellent. I just received my AB set the other day…

The later scheme B&O F3 ( or fake F7) is a MTH dummy unit I repainted…I will run it with the new MTH F3 set…

Tom